The present invention is directed to an apparatus for controlling and monitoring actuators with an open/close characteristic, which apparatus consists of a drive switch unit for actuating a drive force unit, at least one limit or position signal generator that detects an end position of the actuator and an apparatus for actuating the drive switch unit as well as for outputting the limit signal generator state.
In the field of process automation, there are many developments that enable the realization of new possibilities for communicating with field apparatuses and, thus, of an improved controlling, savings of cost and fault monitoring. Thus, on the one hand, a quasi-analog method, already widely distributed, is given by the Highway Addressable Remote Transducer Field communication protocol or HART-field communication protocol, in which the digital signal with a mean value is superposed on a conventional analog signal. The apparatus operating according to the HART-field communications protocol can, without alteration, replace conventional processing apparatuses. On the other hand, great progress has been made in the use of purely digital process apparatuses that communicate with one another via a digital field bus. A digital field bus thereby enables, above all in a large processing installation, a considerable savings in the cost due to reduction in cabling expenses. However, it does have the disadvantage that convention analog apparatuses and field bus apparatuses cannot be exchanged with one another and the installation of the field bus system entails large investments and changes. Nonetheless, in particular for measuring transducers and controllers, such as, for example, position regulators on actuators, many field bus communication process apparatuses or HART-field communication process apparatuses are already available.
The preponderant number of actuators that are currently in use or will be used in the near future have an open/close characteristic, for which field bus communication process apparatuses or HART-field communication process apparatuses are however mostly too costly.
A large number of these controlling apparatuses with an open/close characteristic respectively operate with a drive switch unit for controlling a drive force unit and with at least one limit signal generator that detects an end position.
A typical apparatus for controlling and monitoring an actuator with an open/close characteristic according to the prior art is illustrated in FIG. 2. In these systems, an actuator drive unit (not shown), for example a pneumatic drive, is controlled by a drive switch unit in the form of a solenoid valve 9 and two limit signal generators 11 and 13. For the driving of the solenoid valve 9 and for the outputting of the limit signal generator states, specific apparatuses, such as a disconnecting or isolating amplifier 33 for the one limit signal generator 11, a control valve module 35 for the solenoid valve 9 and a disconnecting or isolating amplifier 37 for the other limit signal generators 13, are additionally provided and are respectively connected via separate cables 39, 41 and 43 with the limit signal generators 11 and 13 and with the solenoid valve 9, which are often arranged in an area in which there is a danger of explosion. The existence of the explosion-threatened area thereby militates against the integration into one unit of the apparatuses 33, 35 and 37 with the solenoid valve 9 and the limit signal generators 11 and 13. Thus, the known apparatuses for controlling and monitoring the actuators with an open/close characteristic are connected, in particular, with a high cabling expense.